PROJECT SUMMARY Cholesterol has been linked to several cardiac and brain vascular diseases, dementias, diabetes, and cancer. Emerging data suggests that such diseases can be traced back to an imbalance in cholesterol transport mediated by high-density lipoproteins (HDLs), specifically attributed to reduced amount and function of native HDLs. As such, synthetic HDL nanoparticles (HDL NPs) have been proposed as next-generation therapeutics for treating these diseases. However, because the development of materials has lagged far behind the pace of biological discovery and understanding, costly failures in the clinic have resulted, reinforcing the desperate need for new approaches to HDL-inspired therapies. To be successful, synthetic HDL NPs must accurately mimic native HDLs in size, shape, cholesterol-uptake capacity, and functional capacity required to manipulate and transport cellular cholesterol in an effective manner. To this end, we are seeking to develop, for the first time, a synthetic strategy to tune HDL NPs so that their form and function can be exquisitely and optimally manipulated around a set of parameters defined by native HDLs. To that end, we have constructed a bio- inspired HDL NP mimetic by assembling the HDL-defining apolipoprotein A-I (apo A-I) and phospholipids around multifunctional organic core (MOC) templates. This approach appears to be highly promising, as these organic HDL NPs (OHDL NPs) closely mimic natural HDLs in their size (~10 nm) and ability to efflux cholesterol from lipid-laden macrophages. Here we propose to optimize the synthesis and purification of OHDL NPs, through modulation of the MOC and downstream synthetic steps, characterize the OHDL NPs, quantify the ability of OHDL NPs to efflux and influx cholesterol and reduce inflammation in vitro, and reduce atherosclerotic plaque burden in a mouse model of atherosclerosis. Through these studies we will generate an optimal OHDL NP therapeutic for the modulation of cholesterol flux, and demonstrate both in vitro and in vivo the efficacy of OHDL NPs at reducing inflammation and atherosclerotic plaque formation.